001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.math.distribution;
018    
019    
020    /**
021     * Interface representing the Poisson Distribution.
022     *
023     * <p>
024     * References:
025     * <ul>
026     * <li><a href="http://mathworld.wolfram.com/PoissonDistribution.html">
027     * Poisson distribution</a></li>
028     * </ul>
029     * </p>
030     *
031     * @version $Id: PoissonDistribution.java 1178295 2011-10-03 04:36:27Z psteitz $
032     */
033    public interface PoissonDistribution extends IntegerDistribution {
034        /**
035         * Get the mean for the distribution.
036         *
037         * @return the mean for the distribution.
038         */
039        double getMean();
040    
041        /**
042         * Calculates the Poisson distribution function using a normal approximation.
043         *
044         * @param x the upper bound, inclusive
045         * @return the distribution function value calculated using a normal approximation
046         */
047        double normalApproximateProbability(int x) ;
048    }